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[78.144.121.210]) by smtp.gmail.com with ESMTPSA id l6sm12132737wib.18.2015.07.20.07.43.58 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 20 Jul 2015 07:43:59 -0700 (PDT) From: Srinivas Kandagatla To: linux-arm-kernel@lists.infradead.org, Greg Kroah-Hartman Cc: Rob Herring , Mark Brown , s.hauer@pengutronix.de, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org, arnd@arndb.de, sboyd@codeaurora.org, pantelis.antoniou@konsulko.com, mporter@konsulko.com, stefan.wahren@i2se.com, wxt@rock-chips.com, Srinivas Kandagatla Subject: [PATCH v8 5/9] Documentation: nvmem: add nvmem api level and how-to doc Date: Mon, 20 Jul 2015 15:43:55 +0100 Message-Id: <1437403435-4306-1-git-send-email-srinivas.kandagatla@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1437403352-4091-1-git-send-email-srinivas.kandagatla@linaro.org> References: <1437403352-4091-1-git-send-email-srinivas.kandagatla@linaro.org> Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This patch add basic how-to and api summary documentation for simple NVMEM framework. Signed-off-by: Srinivas Kandagatla --- Documentation/nvmem/nvmem.txt | 152 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 152 insertions(+) create mode 100644 Documentation/nvmem/nvmem.txt diff --git a/Documentation/nvmem/nvmem.txt b/Documentation/nvmem/nvmem.txt new file mode 100644 index 0000000..dbd40d8 --- /dev/null +++ b/Documentation/nvmem/nvmem.txt @@ -0,0 +1,152 @@ + NVMEM SUBSYSTEM + Srinivas Kandagatla + +This document explains the NVMEM Framework along with the APIs provided, +and how to use it. + +1. Introduction +=============== +*NVMEM* is the abbreviation for Non Volatile Memory layer. It is used to +retrieve configuration of SOC or Device specific data from non volatile +memories like eeprom, efuses and so on. + +Before this framework existed, NVMEM drivers like eeprom were stored in +drivers/misc, where they all had to duplicate pretty much the same code to +register a sysfs file, allow in-kernel users to access the content of the +devices they were driving, etc. + +This was also a problem as far as other in-kernel users were involved, since +the solutions used were pretty much different from one driver to another, there +was a rather big abstraction leak. + +This framework aims at solve these problems. It also introduces DT +representation for consumer devices to go get the data they require (MAC +Addresses, SoC/Revision ID, part numbers, and so on) from the NVMEMs. This +framework is based on regmap, so that most of the abstraction available in +regmap can be reused, across multiple types of buses. + +NVMEM Providers ++++++++++++++++ + +NVMEM provider refers to an entity that implements methods to initialize, read +and write the non-volatile memory. + +2. Registering/Unregistering the NVMEM provider +=============================================== + +A NVMEM provider can register with NVMEM core by supplying relevant +nvmem configuration to nvmem_register(), on success core would return a valid +nvmem_device pointer. + +nvmem_unregister(nvmem) is used to unregister a previously registered provider. + +For example, a simple qfprom case: + +static struct nvmem_config econfig = { + .name = "qfprom", + .owner = THIS_MODULE, +}; + +static int qfprom_probe(struct platform_device *pdev) +{ + ... + econfig.dev = &pdev->dev; + nvmem = nvmem_register(&econfig); + ... +} + +It is mandatory that the NVMEM provider has a regmap associated with its +struct device. Failure to do would return error code from nvmem_register(). + +NVMEM Consumers ++++++++++++++++ + +NVMEM consumers are the entities which make use of the NVMEM provider to +read from and to NVMEM. + +3. NVMEM cell based consumer APIs +================================= + +NVMEM cells are the data entries/fields in the NVMEM. +The NVMEM framework provides 3 APIs to read/write NVMEM cells. + +struct nvmem_cell *nvmem_cell_get(struct device *dev, const char *name); +struct nvmem_cell *devm_nvmem_cell_get(struct device *dev, const char *name); + +void nvmem_cell_put(struct nvmem_cell *cell); +void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell); + +void *nvmem_cell_read(struct nvmem_cell *cell, ssize_t *len); +int nvmem_cell_write(struct nvmem_cell *cell, void *buf, ssize_t len); + +*nvmem_cell_get() apis will get a reference to nvmem cell for a given id, +and nvmem_cell_read/write() can then read or write to the cell. +Once the usage of the cell is finished the consumer should call *nvmem_cell_put() +to free all the allocation memory for the cell. + +4. Direct NVMEM device based consumer APIs +========================================== + +In some instances it is necessary to directly read/write the NVMEM. +To facilitate such consumers NVMEM framework provides below apis. + +struct nvmem_device *nvmem_device_get(struct device *dev, const char *name); +struct nvmem_device *devm_nvmem_device_get(struct device *dev, + const char *name); +void nvmem_device_put(struct nvmem_device *nvmem); +int nvmem_device_read(struct nvmem_device *nvmem, unsigned int offset, + size_t bytes, void *buf); +int nvmem_device_write(struct nvmem_device *nvmem, unsigned int offset, + size_t bytes, void *buf); +int nvmem_device_cell_read(struct nvmem_device *nvmem, + struct nvmem_cell_info *info, void *buf); +int nvmem_device_cell_write(struct nvmem_device *nvmem, + struct nvmem_cell_info *info, void *buf); + +Before the consumers can read/write NVMEM directly, it should get hold +of nvmem_controller from one of the *nvmem_device_get() api. + +The difference between these apis and cell based apis is that these apis always +take nvmem_device as parameter. + +5. Releasing a reference to the NVMEM +===================================== + +When a consumers no longer needs the NVMEM, it has to release the reference +to the NVMEM it has obtained using the APIs mentioned in the above section. +The NVMEM framework provides 2 APIs to release a reference to the NVMEM. + +void nvmem_cell_put(struct nvmem_cell *cell); +void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell); +void nvmem_device_put(struct nvmem_device *nvmem); +void devm_nvmem_device_put(struct device *dev, struct nvmem_device *nvmem); + +Both these APIs are used to release a reference to the NVMEM and +devm_nvmem_cell_put and devm_nvmem_device_put destroys the devres associated +with this NVMEM. + +Userspace ++++++++++ + +6. Userspace binary interface +============================== + +Userspace can read/write the raw NVMEM file located at +/sys/bus/nvmem/devices/*/nvmem + +ex: + +hexdump /sys/bus/nvmem/devices/qfprom0/nvmem + +0000000 0000 0000 0000 0000 0000 0000 0000 0000 +* +00000a0 db10 2240 0000 e000 0c00 0c00 0000 0c00 +0000000 0000 0000 0000 0000 0000 0000 0000 0000 +... +* +0001000 + +7. DeviceTree Binding +===================== + +See Documentation/devicetree/bindings/nvmem/nvmem.txt